This invention relates to a method and apparatus for use in the conversion or rectification of an AC supply to provide a DC output. The apparatus may form part of, for example, a power supply for an electrical or electronic device.
The use of a bridge rectifier to rectify an AC signal, producing a varying DC output is well known. One disadvantage associated with the use of bridge rectifiers is that the DC output varies significantly, varying between substantially the peak input AC magnitude and zero. One technique that is commonly used to reduce the variation in the output signal is to provide a smoothing capacitor connected across the output of the bridge rectifier, the capacitor charging and discharging in use to smooth the output signal. Whilst the provision of such a smoothing capacitor operates satisfactorily in many applications, there is still a significant output variation or ripple. Furthermore, the capacitor must typically be relatively large, both in terms of its capacitance and in terms of its dimensions. As a result, accommodation of such a capacitor in some applications may be challenging.
The power factor of arrangements of the type outlined hereinbefore is typically relatively low, for example in the region of 0.3 to 0.6. Furthermore, where used in medium or high voltage applications, especially those in which the associated load has to be switched, the generation of harmonics can result in the need to provide additional circuitry to suppress such harmonics, adding additional complexity and expense to the arrangement.